The standard of so-called Long Term Evolution (LTE) system, as a next-generation cellular system after the Universal Mobile Telecommunication System (UMTS) based on W-CDMA, is being developed under the Third Generation Partnership (3GPP). In the uplink of LTE system, data transmission based on random access is performed in addition to data transmission based on a schedule, as in the current Wideband Code Division Multiple Access (W-CDMA) (refer to 3GPP TR25.814, for example).
Random access is used, for example, in initial access when the terminal accesses the base station for the first time, such as at power-on, in initial access to a hand-over destination base station when the terminal performs a hand-over to the adjacent cell, in a transition from an idle state to an active state, when synchronization is restored in the active state, and the like.
In random access, all terminals each are basically permitted to send a random access signal simultaneously. Accordingly, the random access signals sent from the terminals simultaneously can cause collision at the base station. A terminal which sent a random access signal that has been received by the base station and has survived the collision can continue subsequent processing. A terminal which sent a random access signal that has not been received successfully by the base station because of a signal collision error sends a random access signal again.
It is assumed that a plurality of terminals each will send a random access signal simultaneously and that signal collision will occur. A terminal which sent a random access signal that has not been received successfully by the base station because of collision needs to perform retransmission. This means that transmission processing time of the random access signal is prolonged and affects the time the terminal needs to access the base station.
Random access in a hand-over to an adjacent cell needs to be performed in a shorter period than random access in initial access such as at power-on. Especially, in a hand-over during a voice call, it is important that access to the hand-over destination base station be completed in a short period, so that voice will not be interrupted nor interrupted in an unacceptably long time.
The possibility that the random access signal sent from the terminal in a hand-over is not received successfully by the base station because of collision needs to be reduced.